Friction materials (disc brake pads, drum brake linings, clutch facings, etc.) for brakes and clutches generally contain a fibrous reinforcement such as organic fibers, inorganic fibers, metal fibers, etc., a thermosetting resin binder such as a phenolic resin, etc., and a filler such as a friction modifier (resin dust, rubber dust or the like), a solid lubricant (graphite, molybdenum disulfide and the like), etc., as the main components.
As the fibrous reinforcement, asbestos was conventionally used for such friction materials for a long time. However, asbestos, which is a carcinogenic substance presents safety and health problems during both manufacture and use. Under these circumstances, non-asbestos friction materials without asbestos have been widely used. In such non-asbestos friction materials, as the fibrous reinforcement, fibrillated aramid fibers (aramid pulp) or a combination of the aramid fibers and glass fibers have been widely used.
Fibrillated aramid fibers have the features that they have a light weight and a high strength as compared with metal fibers, etc., and have a high heat resistance in spite of organic fibers. However, because the aramid fibers are generally expensive, there is a problem that the friction materials using the aramid fibers have a large disadvantage in cost as compared with asbestos series friction materials. Accordingly, there is a need for non-asbestos friction materials having the same performance in heat resistance, mechanical strength, etc., as the friction material with the aramid fibers. But non-asbestos friction materials satisfying all of thermal and mechanical strength, effectiveness, fade characteristics, friction characteristics, etc., and cost have not yet been developed.